I remember some one later asked the same question but can't find it, also you trick don't work fine fore me iTunes Display Duplicate worked buggy for me.
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Am1rr3zASep 15 '10 at 12:40

I was also sure someone already posted this question, but I, too, cannot find it anymore. At least, I'm not crazy ! I know the built-in functionality is a buggy, that's why I added links to 3rd-party softwares.
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StuderSep 15 '10 at 13:40

Another alternative I can highly recommend: Dupin
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ChealionSep 15 '10 at 17:09

1

I was aware of this option, but wanted an automatic way to remove the duplicates
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AragornSep 16 '10 at 2:39

This approach (at least as of 10.5.1) will not do what the questions asks: songs do not need to have the "same encoding" to be recognized as duplicates.
–
raxacoricofallapatoriusNov 15 '11 at 18:41

If you enable iTunes Match, duplicates will now be marked with an icon:

Note however that such files do not need to have the "same encoding" to be recognized as duplicates. Also note that (inconveniently) the file marked by Match as a duplicate (and thus "skipped") may not have the "best" encoding of the duplicated files. For example, you might see this:

In this case, in order to end up with a single song, managed by Match, with the high bit-rate song on your machine, you will need to delete both songs, leaving just the one managed by Match (the first one above)

I haven't tried DupeGuru yet, but iDupe worked quite well for me, though I had to batch up my checkin. First I'd select iTune's buggy "display dupes" and then I'd use that selection to run iDupe on. This sped things up quite a bit. I'm interested to see whether DupeGuru improves things by checking audio finger prints.